In general, a prepreg used for a printed wiring board is formed by impregnating a base material such as glass cloth or the like with a varnish made of a thermosetting resin such as epoxy resin, cyanate resin or the like and then drying it by heating with being reacted. By using the thus formed prepreg, copper clad laminates, printed wiring boards and the like are manufactured.
When the resin constituting the prepreg is in an uncured state, there is a problem in that the surface of the prepreg becomes tacky (that is, tack is developed) so that workability is lowered. Further, there is also a problem in that excessive resin flow occurs when the prepregs are heated and pressed during laminating so that moldability is lowered.
To address such problems, practically, the thermosetting resin constituting the prepreg is cured to a semi-cured state in the above-mentioned heating and reacting process, to thereby suppress development of tack on the surface of the prepreg and control resin flow when the prepregs are heated and pressed during laminating.
However, a problem exists with such a prepreg in a semi-cured state in that it is susceptible to cracking because of its lack of flexibility. As a result, such a semi-cured state prepreg can not be directly subjected to circuit formation processing.
Another problem also exists with such a semi-cured state prepreg in that dust of the resin and the base material is generated during cutting of the prepreg because of poor adhesive strength between the semi-cured resin and the base material, which also results in a lowered workability. In addition, there is also a problem in that such dust comes off the prepreg in handling the prepreg for manufacturing a laminate, and then it is likely to be attached to a metallic foil such as copper foil as well as to a metallic plate used in lamination molding, so that so-called pits and dents are produced on molded laminates and printed wiring boards.
Consequently, a resin material which can be used to form a prepreg which can be directly subjected to circuit formation processing even in the case where the prepreg is in an uncured state or a semi-cured state has not yet been existed. Further, an idea that an uncured state prepreg or a semi-cured state prepreg is made to undergo circuit formation processing and the like as it is has not been conceived until now.